Speed controlled brake



Jan. 4, 1938. T. TARISIEN Re. 20,613

5 FEED CONTROLLED BRAKE Original Filed June 16, 1934 2 Sheets-Sheet l INVEN TOR THEOPHILE TARISIEN I BY Wzfi A TTORNE Y amedamaiess UNITEDSTATES [PATENT OFFICE mammalian-salami, serlall ia'lafi' llune mlm'reisslellaylklfitserialflalm In momenta-7,1,33-

17 Claims.

This invention relates to fluid pressure braking apparatus for railwayor other vehicles'of the kind in which the supply of fluid underpressure to and its release from the brake cylinder or cylinders of theapparatus is arranged to be controlled by a brake valve either directlyor indirectly by varying the pressure obtaining in a brake pipe, theinvention having for its object to provide improved arrangements wherebythe braking action obtained by the operation of the brake valve may becontrolled in accordance with the speed of the vehicle so as to ensurethat the braking eflort exerted shall not exceed that corresponding tothe maximum coefllcient' of friction between the brake blocks and thewheels at any speed, and thus prevent the possibility of the wheelsbecoming locked at any time during the retardation of the vehicle.

In order to bring the vehicle to rest in the shortest possible time, itis essential that the tangential efiort exerted upon the vehicle wheelsby the action of the brake blocks should remain substantially constantas the speed of rotation varies, and to obtain this result it isevidently necessary that the brake cylinder pressure must be adjusted inaccordance with the coemcient of friction obtaining at any time duringthe retardation, and thus in accordance with the speed of the vehicle.

According to the principal feature of the present invention the pressureobtaining in the brake cylinder during an application of the brakes isarranged to be automatically adjusted in accordance with the speed ofthe vehicle in such a manner that when an application of the brakes iseffected the supply of fluid under pressure to the brake cylinder isautomatically cut oil? as soon as a brake cylinder pressure isestablished corresponding to the maximum tangential effort exerted uponthe vehicle wheels by the brake blocks at the speed of rotation of thewheels at the time ofapplication, the supply or fluid under pressure tothe brake cylinder being renewed in the event of a subsequent increasein thespeed of rotation, while the brake cylinder pressure isautomatically reduced as the speed of rotation decreases. a

This control of the braking eflort exerted is furthermore arranged to beeffected without interfering with the application or release of thebrakes to an extent less than that required to produce the maximumretardation above referred to, so that the driver of the vehicle isenabled to retain full control or the braking action while enabling themaximum retardation to be obtainedwithoutthepossibilityotlocklngthewheels or the vehicle.

The invention is illustrated by way of example in the accompanyingdrawings,

Figure 1 or which is a atic view of the invention as applied to fluidpressure braking apparatus of the kind in which the supply of fluid toand its release from the brake cylinder is directly controlled by adriver's brake valve;

Figure 2 being a similar view illustrating the invention as applied tobraking apparatus in which the control of the braking action is effectedby varying the pressure in a brake pipe under the control of the driversbrake valve.

Referring now first to Figure 1, it will be seen that the apparatustherein illustrated comprises an air compressor I of any suitable type,adapted to supply air to a main reservoir 2 through a pipe 3, a pipe 4leading from the reservoir 2 to a driver's brake valve 5 of any suitableconstruction, by the operation of which compressed air from the pipe 4is supplied to a pipe 8 or communication is established between the pipe8 and the atmosphere. The apparatus shown in Figure 1 also comprises aregulating valve I, a speed control device 8, and a brake cylinder 9,the latter when supplied with compressed air being arranged to efiectthe application of brake blocks II to the wheels ll of the vehicle,through any suitable form of brake rigging.

The regulating valve 1 comprises a casing l2, subdivided internally intothree compartments indicated at It, I4 and I5, by means 01' flexiblediaphragms l8, H, which are connected together by means of a rod orspindle is adapted to operate a slide valve [9 arranged in the chamberIS.

The lower part of the casing l2 contains a supply valve of the poppettype, provided with a controlling spring II, the valve 20 controllingcommunication between a supply chamber 22 communicating with the pipe 5by means of a pipe 23 and the chamber Ii.

The central chamber il 01' the regulating valve 1 is in communicationthrough a pipe 24 with the pipe 6, the lower chamber I! being incommunication with the brake-cylinder 9 by means of a pipe 25. The seat25 of the slide valve I! is provided with an exhaust port 21 adaptedwhen uncovered by the slide valve I! to establish communication betweenthe chamber 15 and the atmosphere.

The speed control device 8 may be constituted by an oil or water pump orother form 01 compressor driven as indicated from anaxle 2| oi thevehicle, the fluid pressure developed by the action of the device 2being transmitted through a pipe 29 to the upper chamber lI-ot theregulating valve 1.

The etlective area or the diaphragm l5 the regulating valve I is, asillustrated, less than the effective area of the diaphragm l1, and thelower part of the stem l9 carrying the slide valve I9 is adapted undercertain conditions to engage with the stem 30 of the supply valve 20 soas to open the latter.

The operation of the apparatus is as' follows:

When the vehicle is in motion the operation of the speed control device9 causes a pressure to be established in the chamber i3 01 theregulating valve 1 which is proportional to the speed of rotation of theaxle 29, and thus to the speed of the vehicle, and under runningconditions with the brakes released the diaphragms l8, l1 and their steml8 are moved downward to the position shown under the action of thepressure obtaining in the chamber l3 so that the stem l engages with thestem 30 01 the valve 20 and maintains this valve in its open positionagainst the action of the spring 2|.

Under running conditions it will be understood that the pipe 5 is incommunication with the atmosphere through the drivers brake valve 5 inthe release position of the latter, so that the chamber II is atatmospheric pressure, and since the valve 20 is open the brake cylinder9 is in communication with the chamber 22 which is also in communicationwith the atmosphere by way of the pipes 23 and 5.

When it is desired to effect an application 0! the brakes, the driver'sbrake valve 5 will be operated to cut 011 communication between the pipe5 and the atmosphere, and to establish communication between the pipes 4and i. Compressed air will, under these conditions, be supplied from thereservoir 2 to the pipe 5 and will flow by way of chamber 22 past theopen valve 29 to the chamber I5 and thence by way of pipe 25 to thebrake cylinder 9. Compressed air is also supplied from the pipe 6through pipe 2 to the chamber ll, so that the chambers H and I5 are atthe pressure obtaining in the brake cylinder.

Asthe pressure in the brake cylinder 9 increases the pressure in thechamber ll acting in opposition to the pressure in the chamber l3 willtend to move the diaphragms l6, l1 upward so as to permit the valve 20to close under the action of its controlling spring 2|, but so long asthe pressure of the air supplied to the chamber ll through the driver'sbrake valve 5 is insuflicient to overcome the opposing pressure in thechamber i3 the valve 20 will remain open, so that the pressure in thebrake cylinder will be entirely under the control of the driver, who, byoperating the brake valve 5 in the usual manner, can eflfect an increaseor decrease in the brake cylinder pressure, or may maintain thispressure at any desired value.

In order to eflfect the maximum retardation of the vehicle, the driversbrake valve 5 will be maintained in its application position so as tosupply compressedair continuously to the pipe 5, and as soon as thepressure obtaining in the chamber l4 exceeds that obtaining in thechamber II the disphragms l5, II will be moved from the position shownin Figure 1, to a position in which the supply valve 25 is permitted toclose, thereby cutting oi the further supply of air to the brakecylinder 9 from the chamber I5.

The value of the brake cylinder pressure at which the iurther supply ofcompressed air to the brake cylinder is thus interrupted will evidentlydepend upon the pressure in the chamber I 3, and thus upon the speed oi.rotation of the axle 29 of'the vehicle, and the pressure developedcorresponds to the maximum tangential retarding effort upon the vehiclefor the coefficient 01' friction between the brake blocks l0 and thewheels ll of the vehicle at that speed.

In the event of the speed of the vehicle increasing for any reason afterthe brakes are thus applied the increased pressure in the chamber I!will cause the diaphragms l5, I"! again to move downwards, therebyreopening the valve 20 and permitting the further suppEy of compressedair to the brake cylinder 9 to increase the braking pressure to anextent corresponding to the increased speed.

If, however, as is more usually the case, the speed of the vehicledecreases owing to the application of the brakes the pressure in thechamber l3 will correspondingly decrease with the result that the brakecylinder pressure obtaining in the chamber l5 will cause the diaphragmsl5, II to move upwards to an extent sufllcient to cause the slide valvel9 to uncover the exhaust port 21 and thereby permit the brake cylinderpressure to be reduced by the flow 01' air through the pipe 25, chamberi5 and exhaust port 21.

The brake cylinder pressure is thus reduced until, owing to thecorresponding reduction of pressure in the chamber IS, the diaphragmsl6, l1 again move downwards to the position shown, thereby cutting of!the further release of air from the brake cylinder, and this action willbe continued as the speed of the vehicle decreases so that at all timesthe brake cylinder pressure corresponds to that required to produce themaximum retarding tangential effort on the vehicle without locking thewheels.

During the retardation of the vehicle as above explained, the driversbrake valve 5 may be operated to reduce the braking action byestablishing communication between the pipe 5 and the atmosphere,whereupon the corresponding reduction of pressure in the chamber ll dueto the release of air by way of the pipe 24 will cause the diaphragmsl6, IT to move downwards, thereby opening the valve 25 and permittingthe flow of air from the brake cylinder 9 to the atmosphere,

under the control 01 the driver, by way of pipe 25,

pressure to and its release from the brake cylinder 9 is in this casecontrolled by means of a triple valve 3| associated with the usualauxiliary reservoir 32 and operated in accordance with the pressureconditions obtaining in a brake pipe 33, the pressure in which iscontrolled by means of the driver's brake valve, not shown. An auxiliarybrake cylinder 24 is provided which is suitably coupled, as shown, tothe brake rigging operated by the brake cylinder 9, the brake cylinder34 being connected by means 0! a pipe 25 to the chamber I 5 of theregulating valve 1.

The apparatus also comprises a speed control device 5 similar to thatshown in Figure 1, communicating by means of a pipe 29 with the upperchamber II of the regulating valve 1. A pipe 95 leading from the triplevalve 9| communicates and pipe II.

some I Acut-oil'vaivedeviceIlisprovidedcompriringanupperchamberflcommunicatingwith meansofaiiexiblediaphragmllthechamber aneahaustportll.

is connected tovalves II, II controllingcommunicaflonrespectivelybetweenthechamberIIandachamberll,andbetweenthislatterchamher and a chamber II, whichcommunicates by way of a pipe II with a supplementary reservoir pipewitharetainingvalvedevieeflcontaining a spring-controlled non-returnvalve II which controls communication between the pipe II and apipelileadingtothebranchpipe II oi'the' The brake cylinder I being atatmospheric pressure the chamber II of the cut-oil valve device is alsoat atmospheric pressure, with the result that the valve II is maintainedclosed and the valve II open under the action of the con-- trollingspring II. The chamber ll of the valve device II and the supply chamber22 of the regulating valve I are thus also in communication with theatmosphere by way of chamber II and the exhaust port 4|.

80 long as the vehicle is in motion, the c ber II of the regulatingvalve I ismaintained at a pressure corresponding'to the speed oi! thevehicle, and the valve II being thus maintained open in the same manneras that already described with reference to Figure 1, the auxiliarybrake cylinder I4 is in communication with the atmosphere by way of pipe25, chamber II, and supply chamber II 01' the regulating valve 1.

When it is required to eiiect an application of the brakes, the pressureiii the brake pipe II 'is' reduced by the operation of the driver'sbrake valve in the usual manner. so that compressed air is supplied tothe brake cylinder I from the auxiliary reservoir I2 through the triplevalve Ii. The pressure obtaining in the brake cylinder I is transmittedthrough the pipe I! to the chamber II of the cut-ofl valve device I1,and the diaphragm II is thereby moved downwards to close the valve 42and open the valve II. Communication between the pipe II and theatmosphere is cut oil by the closure 01' the valve 42, and the openingof the valve II establishes communication between the supplementaryreservoir 41 and the pipe II by way of pipe II and chamber II.Compressed air is thereupon supplied from the supplementary reservoir IIthrough the cut-oil valve I! to pipe II and supply chamber 22 0! the.

regulating valve I, and from the chamber 22 air flows past the openvalve III to the chamber II of the regulating valve I and through pipeII to the auxiliary brake cylinder II.

It will thus be seen that the pressure in the chamber N of theregulating valve 1 tending to movethe'll. W sureobtainiminthebnhcyllnd lthus dependent upon the degree 0! brakingapplicatloneii'ectedbytheactimiolthetriple 'vaive II. thepipeIlandseparated frosn'a chamber II by I 'lhepressure in'the chamber ll ofthe regulatingvalveltendingtomovethediaphragms II, "upwards is dependentupon the pressure obtaining in the auxiliary brake cylinder II, and thesupply of air to this brake cylinder is thuscontrolledbytheregulatingvalveinthemanner already in accordance with thepressure obtaininginthechamber II whichisinturndependentuponthespeedotthevehicle.

The total braking eii'ort obtained will evidentlybeduetothesumoi'thebrakingeii'ortsotthe brake cylinders I and II, thesupply oi compressed air to and its release from the brake cylinder Ibeing under the dirct control of the triple valve II while theadditional braking eii'ort due to the auxiliary brake cylinder II iscontrolled by the regulatingvalve'linsuchamannerastobe dependent uponthe speed of the vehicle during the braking application.

when the brakes are released the brake cylinder I is vented through thetriple valve II in the usual manner and the reduction 01 pressure in thechamber II of the cut-oil valve device 31 etiects the opening oi. thevalve I2, thereby permitting air to be released from the auxiliary brakecylinder II through pipe 25, chamber i5, past the valve 2|,- supplychamber 22, pipe II, chambers 44 and II, and exhaust port ll.-

While the invention has been described above as applied to brakingapparatus operated by compressed air. it will be evident that bysuitable alteration in the construction and arrangement of theregulating valve and of the device by which its controlling pressuredependent upon the speed of the vehicle is obtained, the invention maybe applied to vacuum braking apparatus as will be obvious to thoseskilled in the art.

The invention is evidently not limited to the particular arrangement orconstruction of the various valve devices above described andillustrated by way of example, and modifications in these and otherrespects may evidently be made without exceeding the scope of theinvention.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. In a fluid pressure brake for a vehicle, the combination with abrakecylinder, of manually controlled means for effecting the supply offluid under pressure to the brake cylinder, means operative to establisha fluid pressure which pressure is proportional to the speed of avehicle wheel, a brake controlling valve device comprising valve meansfor controlling the supply of fluid under pressure to the brakecylinder, a first movable abutment subject to the opposing pressures ofthe brake cylinder and the pressure of fluid supplied to effect anapplication of the brakes for operating said valve means, and a secondmovable abutment subject to the opposing pressures of the fluid suppliedto effect an application of the brakes and to said fluid pressure whichis proportional to the speed of the vehicle. said last named movableabutment also controlling the operation of said valve device.

2. In a fluid pressure brake for a. vehicle. the combination with abrake cylinder, of manually controlled means for eilecting the supplyoi. fluid under pressure to the brake cylinder, a brake controllingvalve device comprising valve means for controlling the supply of fluidunder pressure to the .brake cylinder, a flrst movable abutment subjectto the opposing pressures oi the brake cylinder and the pressure offluid supplied to eflect an application of the brakes for operating saidvalve means, and a second movable abutment operated by. fluid underpressure for also controlling the operation of said valve device, andmeans controlled according to the speed of a vehicle wheel for varyingthe fluid pressure on said second abutment, the flrst abutment beinurged by-the brake cylinder fluid pressure in a direction to eflfectmovement of the valve means in a direction to cut of! the flow oi fluidto the brake cylinder.

3. In a fluid pressure brake for a vehicle, the combination with a brakecylinder, of manually controlled means for eflecting the supply of fluidunder pressure to the brake cylinder, a brake controlling valve devicecomprising valve means for controlling the supply of fluid underpressure to the brake cylinder, a first movable abutment subject to theopposing pressures of the brake cylinder and the pressure of fluidsupplied to effect an application of the brakes for operating said valvemeans, and a second movable abutment operated by fluid under pressurefor also controlling the operation of said valve device, and meanscontrolled according to the speed of a vehicle wheel for varying thefluid pressure on said second abutment, the first abutment being urgedby the pressure of fluid supplied to effect an application of the brakesand the second abutment being urged by the fluid pressure which isvaried according to the speed of the vehicle wheel in a direction toefl'ect movement or the valve means in a direction to open thecommunication through which fluid is supplied to the brake cylinder.

4. In a fluid pressure brake for a vehicle, the combination with a brakecylinder, of manually controlled means for effecting the supply oi fluidunder pressure to the brake cylinder, a brake controlling valve devicecomprising valve means for controlling the supply 01' fluid underpressure to the brake cylinder, a first movable abutment subject to theopposing pressures oi the brake cylinder and the pressure of fluidsupplied to efl'ect an application of the brakes for operating saidvalve means, and a second movable abutment operated by fluid underpressure for also controlling the operation of said valve device, andmeans controlled according to the speed 01' a vehicle wheel for varyingthe fluid pressure on said second abutment, the first abutment beingurged by the pressure of fluid supplied to eilect an application 01 thebrakes and the second abutment being urged by the fluid pressure whichis proportional to the speed of the vehicle wheel to move in a directionto effect movement of the valve means to open the communication throughwhich fluid is supplied to the brake cylinder, movement of said valvedevice in this direction being opposed by the pressure oi. the fluid inthe brake cylinder on the first abutment.

5. In a fluid pressure brake for a vehicle, the combination with a brakecylinder, of manually controlledmeans tor eflecting the supply of fluidunder pressure to the brake cylinder, means operative to establish afluid pressure which pressure is proportional to the speed of a vehiclewheel, a brake controlling valve device comprising valve means forcontrolling the supply of fluid under pressure to the brake cylinder, a

- flrst movable abutment subject to'the opposing pressures oi! the brakecylinder and the pressure of fluid supplied to eflect an application 01'the brakes for operating said valve means, and a second movable abutmentsubject to the opposing pressures of the fluid supplied to effect anapplication of the brakes and to said fluid pressure which isproportional to the speed of the vehicle wheel, said last named movableabutment also controlling the operation of said valve device, the brakecylinder fluid pressure operating on the flrst abutment and the pressureof fluid supplied to effect an application of the brakes operating onthe second abutment being operable to urge said abutments in a directionto eifect movement of the valve means in a direction to close thecommunication through which fluid is supplied to the brake cylinder, the

fluid pressure proportional to the speed of the vehicle and operable onthe second abutment, and the pressure of fluid supplied to eflect anapplication of the brakes and operating on the first abutment beingoperable to urge said abutments in a direction to efiect movement of thevalve means in a direction to open the communication through which fluidis supplied to the brake cylinder. 6. In a fluid pressure brake for avehicle, the combination with a brake cylinder, of manually controlledmeans for effecting the supply of fluid under pressure to the brakecylinder, means aperative to establish a fluid pressure which pressureis proportional to the speed of a vehicle wheel, a brake controllingvalve device comprising valve means for controlling the supply of fluidunder pressure to the brake cylinder, said valve means also controllinga communication through which fluid is released from the brake cylinder,a first movable abutment subject to the opposing pressures of the brakecylinder and the pressure of the fluid supplied to effect an applicationof the brakes for operating said valve means, and a second movableabutment subject to the opposing pressures of the fluid supplied toeflect an application of the brakes and to the fluid pressure which isproportional to the speed of the vehicle wheel, said last named abutmentalso controlling the operation of said valve means, the flrst abutmentbeing urged by the pressure of fluid supplied to effect an applicationof the brakes and the second abutment being urged by the fluid pressurewhich is proportional to the speed of the vehicle wheel to move in adirection to eflect movement of the valve means in a direction to openthe communication through which fluid is supplied to the brake cylinderand to close the communication through which fluid is released from thebrake cylinder, the first abutment being urged by the brake cylinderfluid pressure and the second abutment being urged by the pressure offluid supplied to efiect an application. of the brakes to move in adirection to eflect movement of the valve means in a direction to closethe communication through which fluid is supplied to the brake cylinderand to open the communication through which fluid is released from thebrake cylinder.

7. In a fluid pressure brake for a vehicle, in combination, a valve forcontrolling the supply fluid under pressure to the brake cylinder, amovable abutment operated by an increase in fluid pressure for openingsaid valve, another movable abutment operated by an increase in fluidpressure for opening said valve, manually operated means for supplyingfluid under pressure to some the first abutment, and means for supplyingfluid under pressure to the second abutment at a pressure correspondingwith the speed of a vehicle wheel.

8. In a fluid pressure brake for a vehicle, in combination, a valve forcontrolling the supply of fluidunder pressure to the brake cylinder, amovable abutment operated by an increase in fluid pressure for openingsaid valve, manually operated means for controlling the supply 01' fluidunder pressure to and its release from the brake cylinder past saidvalve, another movable abutment operated by an increase in fluidpressure for opening said valve, means controlled by said manuallyoperated means for supplying fluid under pressure to the first abutment,and means for supplying fluid under pressure to the second abutment at apressure corresponding with the speed of a vehicle wheel.

9. In a vehicle brake system, in combination, a valve device havingspaced mbvable abutments and a chamber for and to one side of eachabutment, said valve device being operable upon supply of fluid underpressure to one of said chambers to effect an application of the brakes,and operable upon establishment of and variation of pressure in theother of said chambers, while the pressure in said first chamber remainsunvaried, to vary the degree of application of the brakes, and meansoperable to establish and vary the pressure in said other chamberaccording to a variable operating condition of the vehicle.

10. In a vehicle brake system, in combination, a valve device having twomovable abutments of unequal efl'ective pressure areas and a chamber forand to one side of each of said abutments, said valve device beingoperable upon supply of fluid under pressure to one of said chambers toeffect an application of the brakes, and operable upon establishment ofand variation of pressure in the other of said chambers, while thepressure in said first chamber remains unvaried, to vary the degree ofapplication of the-brakes, and means operable to establish and vary thepressure in said other chamber according to a variable operatingcondition of the vehicle.

11. In a vehicle brake system, in combination, a valve device having twoflexible diaphragms of unequal effective pressure areas arranged inspaced relationship and a chamber for and to one side of each of saidabutments, said valve device being operable upon supply 01' fluid underpres sure to one of said chambers to eflect an application of thebrakes, and operable upon establishment of and variation of pressure inthe other or said chambers, while the pressure in said first chamberremains unvaried, to vary the degree of application the brakes, andmeans operable to establish and vary the pressure in said other chamberaccording to a variable operating condition of the vehicle.

12. In a vehicle brake system, in combination, a valve device having aplurality of spaced flexible diaphragms and a chamber for and to oneside of each of said diaphragms, said valve device being operable .uponsupply of fluid under pressure to one 01' said chambers to effect anapplication of the brakes, and operable upon establishment of andvariation of pressure in the other of said chambers, while the pressurein said first chamber remains unvaried, to vary the degree oi ap- 13. Ina vehicle brake system, in combination, a brake cylinder, a valve devicehaving two flexible diaphragms of unequal effective pressure areas and achamber for and to one side of each of said diaphragms, said valvedevice being operable upon supply of fluid under pressure to one 01 saidchambers to eiIect a supply of fluid under pressure to said brakecylinder, and operable upon establishment of and variation of pressurein the other of said chambers, while the pressure in said first chamberremains unvaried, to vary the degree of brake cylinder pressure, andmeans so constructed and arranged as to establish in said other chambera fluid pressure and to vary said fluid pressure to correspond to avariable operating condition oi! the vehicle.

14. In a vehicle brake system, in combination, a valve device havingspaced movable abutments and a chamber for and to one side of eachabutment, said valve device being operable upon the establishment offluid pressure in both of said chambers at the same time to efiect anapplication of the brakes, and being operable upon the variation ofpressure in one of said chambers while the pressure in the other of saidchambers remains unvaried to vary the degree of the application, andmeans governed by a variable operating condition of the vehicle forcontrolling the pressure of fluid in one of said chambers.

15. In a vehicle brake system, in combination, a valve device havingspaced movable abutments and a chamber for and to one side of eachabutment, said valve device being operable upon the establishment offluid pressure in both of said chambers at the same time to effect anapplication of the brakes, and being operable upon the variation ofpressure in one of said chambers while the pressure in the other of saidchambers remainsunvaried to vary the degree of the application, andmeans governed by the speed of the vehicle for controlling the pressureof fluid in on of said chambers.

16. In a vehicle brake system, in combination, a valve device havingspaced movable abutmentsand a chamber for and to one side of eachabutment, said valve device controlling a communication through whichfluid under pressure is supplied to effect an application of the brakesand through which fluid under pressure is released to effect a releaseof the brakes, and being operable upon the establishment oi fluidpressure in both of said chambers at the same time to so control saidcommunication as to establish a brake application to one degree, andoperable upon the subsequent variation of pressure in one of saidchambers while the pressure in the other of said chambers remainsunvaried to modify the degree ofthe brake application, and meansgoverned by the speed oi the vehicle for controlling the pressure offluid in one of said chambers.

17. Ina vehicle brake system, in combination, a valve device havingspaced movable abutments 01' different eflective pressure areas and achainber for and to one side ofeach abutment, said valve device beingoperable upon the establishment of fluid pressure in both of saidchambers at the same time to eflect an application of the brakes, andbeing operable upon the variation oi pressure in one of said chamberswhile the pressure in the other 01' said chambers remains unvaried tovary the degree of the application, and means governed by a variableoperating condition of the vehicle for controlling the pressure oi fluidin one of said chambers.

THEOPEILE 'IARISIEN.

